Fireplace construction



Oct. 14, 194.1. c. v. cRAiG 2,258,882 FIREPLACE CONSTRUCTION Filed July 15, 1939 //V VEN TOP 0/4/15 I/ GPA/0 Patented Oct. 14, 1941 UNITED STATES PATENT OFFICE FIREPLACE CONSTRUCTION Charles v. Craig, Boise, Idaho Application July 15, 1939, Serial No. 284,768

8 Claims.

This invention relates to building construction and-the like and particularly pertains to a fireplace construction.

, For many generations the open fireplace has been a favorite source of heat in dwellings apparently on account of its beauty and companionable atmosphere. This type of fireplace hasbeen uniformly recognized as being an inefficient source of heat. The main reason for the efiiciency of an open fireplace is due to the .fact that a large vertical sectional area is open to the room above thecombustion zone, and due to the additional fact that the chimney draft draws into the fireplace from the room from twenty to thirty times the amount of air actually needed for combustion and several times the amount of air that is needed for healthful air change in the room. It will thus be recognized that the heat which is imparted to the air in the roomisdissipated and lost due to the fact that it is drawn into the chimney from the room in large-and unnecessary volume, and for the additional reason that the chimney air and gases are cooled to temperatures which make the recovery' of .heat by the use of auxiliary heat exchangers difficult. It will also be recognized that in the natural operation of an open fireplace theair currents in the room must fiow toward the fireplace, thus precluding the possibility that any appreciable amount of heat can be carried out'intothe room by direct convection currents. These enumerated conditions have been present in a'va'rying degree in all types of open fireplaces and the only attempts to obtain increased efliciency has been through the use of dampers andchan ges in dimensions of the fireplace opening and the chimney. The net result of these changes in design is that the effective heat from the fireplace is limited to a portion of the radiant heat emitted by the fire and the back and sides 'of. the fireplace. Thus, the amount of radiant heat is limited in quantity and must come from one point in the room; in fact, much of the radiant heat is lost since it is drawn up the chimney. It has been found that approximately two-thirds of all of the heat actually generated by the combustion in the grate of an open fireplace is drawn up the chimney in the form of heated air and gases and serves no useful purpose.

It is the principal object of the present invention to provide a fireplace structure in which a more efficient action of the fireplace is brought about by the use of auxiliary air heating means,

room-into the chimney will be retarded and heat may be imparted to the room by convection air currents. j a 7 1 The present invention contemplates a provision of an open fireplace having '-a grate of desired type and a'fiue in-which air may pass in counter flow, one stream of air being the normal draft stream carrying the gases and products of combustion up the chimney and the other stream of air passing-downwardly in heat exchangerelationship thereto and being used to form a downwardly andoutwardly moving air screen across the mouth of the fireplace open- The invention is illustrated by way of example in the accompanying drawing, in which: Figure-1 is a view in elevation showing an open fireplace provided with a chimney and embodyingthe-features of the present invention. Fig. 2 is a view in central vertical 'section through the fireplace showing the fiue arrangement andthe auxiliary heating structure.

Fig. 3 is a view in transverse section showing the flue.

Referring more particularly to the drawing, I0 indicates a hearth of a fireplace. H indicates the front of a'fireplace formed with the fireplace opening |2 I3 indicates a suitable grate or other 1 structure for supporting or providing materials for combustion. The fireplace opening l2 communicates with a fireplace M, at the top of which is a throat l5 leading to the flue or chimney l6. 7 The chinmey I6 is formed with a central flue pipe or passageway ll directly in communication with the throat and a circumscribingwall I8 spaced therefrom to provide an air passageway [9. The air passageway I9 is designed to direct air downwardly around the flue ll and to a duct which is led down through the cowl 2| of the fireplace and then downwardly within the column of the fireplace as indicated at 22. The lower end of the duct is in communication with a suction fan 23. This fan is of any suitable design and is power driven. It is to be understood that the fan or other air propelling means is of sufficient capacity to produce a substantially complete air curtain across the grate opening by means hereinafter described. It is provided with an outlet pipe 24 which is connected with a vertical pipe 25 extending to a perforated. manifold pipe 26. The manifold pipe 26 is positioned horizontally in the rear of the cowl 2| and at thelower front edge of the throat l5. This pipe is formed with and means whereby the flow of air from the aplurality of perforations throughout its length through which jets of air may be directed in a downwardly and outwardly direction. These perforations may be fitted with jet tubes 2! if desired.

For the purpose of providing auxiliary air for combustion a T-connection 28 is interposed in the length of the pipe 25 and leads to a valve 29 which controls the fiow of air to a nozzle 30. The nozzle 30 is shown in Fig. 1 as projecting in a horizontal direction and at the approximate level of the fuel being burned so that if desired air to support combustion will be provided by the nozzle.

In order to insure thorough and efficient exchange of heat from the products of combustion and gases flowing upwardly throughthe flue l1 and the fresh air which is drawn downwardly through the passageway l9 and to the suction fan 23, staggered baflle plates 3| are mounted within the flue l1 and inclined deflecting plates 32 are mounted in the space l9 to extend in encircling positions around the flue pipe I! and to thus prolong the period of time in which the fresh induction air and the products of combustion and eduction gases are in counter-flow and in heat exchange relationship with each other.

It is to be understood that in order to obtain the highest efiiciency from the radiant heat present in the chimney the pipe I8 is made of sheet metal and acts as a lining for the chimney and the walls of the flue I! are made of sheet metal and provide a conduit through which the heated gases pass. In some instances it might be found desirable to eliminate the use of the sheet metal lining l8 but in any event there will be a countercurrent flow of air and gases in the chimney.

In operation of this invention the structure is designed and assembled substantially as indicated in the drawing and as previously described. The action and efiicient results obtained by the use of the invention can best be demonstrated by the following example.

Assume:

Degrees F. Temperature escaping air and gas at chimney-throat 200 Temperature escaping air and gas at top of chimney 100 Temperature indrawn fresh air at top of chimney 30 Temperature indrawn fresh air at throat of fireplace 90 Volume of each, 200 C. F. M. (room temp.)

The average temp. of the escaping air will then be 150 The average temp. of the incoming air will then be 60 Giving a temperature difference of 90 sq. ft. heat exchange area. Available as a source of this heat would be 52% of the 48,000 B. t. u. in the coal, or 24,960 B. t. u.

F. is a considerably lower temperature than usually used in registers, but on account of the excess amount being heated and the addition of the radiant heat to the room, it would probably be sufficient. This radiant heat should be 20% of 48,000 B. t. u. or 9,600 B. t. u./hr., giving a total, with the 12,960 B. t. u. in the fan discharge, of 22,650 B. t. u. per hr. This is much in excess of the heating load of an ordinary room and unless two or more rooms were to be heated with one fireplace it should not be necessary to burn 4# of coal per hour.

.It will be noted that the chimney gases would not be cooled enough to destroy the chimney draft. The effective size of the chimney would be an inch or two smaller all around, but would remain amply large, especially with the steel construction. The downward velocity would be low (around 600 F. P. M.) and the power requirements of the fan very small. As the air pulled out of the room would be balanced by the warm air coming in, there would be no tendency for the cold air leakage into the room which is so characteristic of fireplace warmed rooms. Modern air-conditioning refinements could be added when desired, such as automatically controlled humidification, thermostatic control of the fan, etc. Where a number of fireplaces would be fired, it would be possible to run both a collecting and a distributing duct to each room, the collecting system under slight vacuum with thermostatcontrolled dampers at each fireplace.

Attention is directed to the fact that by the present arrangement the air which is drawn into the fireplace by the chimney draft is passing at a relatively low velocity due to the large area of the fireplace opening. It is possible to retard and repel the inflow of this air by the projection of the jets of air from the manifold 26. This tends to form a screen of preheated air which projects downwardly and outwardly across the fireplace opening I2, and while supplying air to support combustion prevents an excess amount of air from being drawn in from the room. It is recognized that the air drawn in from the room is cold air, which would tend to cool the chimney gases and that by cutting down the volume of this secondary cold air it is possible to maintain the chimney gases at a higher temperature and to thereby increase the heat exchange temperature imparted to the fresh air which passes down the chimney through the passageway I9. While the air screen produced by the downwardly projecting jets occur substantially over the entire area of the grate opening and in advance of the fire, it will be evident that a normal draft condition will prevail in the fireplace tending to draw air from the room and from the air screen or curtain.

It will thus be seen that the invention here disclosed provides simple means for controlling the combustion of fuel in an open fireplace and means whereby the amount of heat units obtainable from the combustion of a given fuel will be materially increased due to the heat exchange action set up between the chimney gases and a stream of fresh air delivered to the grate for heating purposes, and which air tends to act as a barrier against the inflow of cooler air from the room.

While I have shown the preferred form of my invention it will be understood that various changes may be made in the steps of the process and the parts of the apparatus by-those skilled in the art without departing from the spirit of the invention as claimed.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. A fireplace and the like having a grate opening therein, a flue in communication therewith, and power means for positively projecting jets of air downwardly and across the grate opening to form an air curtain, which is interposed between the air in the room and the combustion area of the grate.

2. A fireplace and the like having a grate opening therein, a flue in communication therewith, means for positively projecting jets of air downwardly and across the grate opening to form an air curtain, which is interposed between the air in the room and the combustion area of the grate, and means for pre-heating the air projected across the grate opening.

3. A grate structure having a combustion area, a grate opening establishing communication between the room and the combustion area, a flue in communication with the grate, said flue being formed with two passageways, one for leading the products of combustion upwardly and away from the grate and the other for delivering fresh air downwardly into the grate to support combustion, and means associated with the second mentioned flue for positively projecting said fresh air across the grate opening to form an air curtain.

4. A grate structure having a combustion area, a grate opening establishing communication between the room and the combustion area, a flue in communication with the grate, said flue being formed with two passageways, one for leading the products of combustion upwardly and away from the grate and the other for delivering fresh air downwardly into the grate to support combustion, said flue passageways being in heat exchange relationship with each other whereby the downwardly moving fresh air will receive heat from the upwardly moving products of combustion, and means associated with the second mentioned flue for positively projecting said fresh air across the grate opening to form an air curtain.

5. A grate structure having a combustion area, a grate opening establishing communication between the room and the combustion area, a flue in communication with the grate, said flue being formed with two passageways, one for leading the products of combustion upwardly and away from the grate and the other for delivering fresh air downwardly into the grate to support combustion, said flue passageways being in heat exchange relationship with each other whereby the downwardly moving fresh air will receive heat from the upwardly moving products of combustion, and mechanical means for drawing the fresh air stream downwardly, and means associated with said mechanical means for projecting jets of the fresh air across the grate opening to form an air curtain.

6. A grate structure having a combustion area, a grate opening establishing communication between the room and the combustion area, a flue in communication with the grate, said flue being formed with two passageways, one for leading the products of combustion upwardly and away from the grate and the other for delivering fresh air downwardly into the grate to support combustion, said flue passageways being in heat exchange relationship with each other whereby the downwardly moving fresh air will receive heat from the upwardly moving products of combustion, mechanical means for drawing the fresh air stream downwardly and projecting said heated fresh air stream across the opening of the grate.

7. A grate structure having a combustion area, a grate opening establishing communication between the room and the combustion area, a flue in communication with the grate, said flue being formed with two passageways, one for leading the products of combustion upwardly and away from the grate and the other for delivering fresh air downwardly into the grate to support combustion, said flue passageways being in heat exchange relationship with each other whereby the downwardly moving fresh air will receive heat from the upwardly moving products of combustion, mechanical means for drawing the fresh air stream downwardly, and means associated with said mechanical means for projecting a plurality of jets of said heated fresh air downwardly and outwardly across the grate opening whereby a barrier will be created to retard the inflow of air from the room to the combustion area of the grate.

8. A grate structure having a combustion area, a grate opening establishing communication between the room and the combustion area, a flue in communication with the grate, said flue being formed with two passageways, one for leading the products of combustion upwardly and away from the grate and the other for deliverifig fresh air downwardly into the grate to support combustion, said flue passageways being in heat exchange relationship with each other whereby the downwardly moving fresh air will receive heat from the upwardly moving products of combustion, mechanical means for drawing the fresh air stream downwardly, means for projecting a plurality of jets of said heated fresh air downwardly and outwardly across the grate opening whereby a barrier will be created to retard the inflow of air from the room to the combustion area of the grate, and separate means for introducing said fresh air into the combustion area.

CHARLES V. CRAIG. 

